1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus which includes a tape transport driving means and a tape guide drum housing therein a rotary magnetic head for forming slant tracks on a magnetic tape and on which the magnetic tape is wrapped in a predetermined angular extent. Also, the present invention relates to a data recording apparatus for recording data on a magnetic tape in a so-called helical-scan system and a reproducing method thereof.
2. Description of the Prior Art
In conventional magnetic recording and reproducing apparatus, a magnetic tape can be transported in the positive and opposite directions but a tape guide drum is rotated only in one direction.
Also, as shown in FIG. 1, consider the case of an artificial satellite orbiting the earth that starts receiving data transmitted from the surface of the earth from a certain point over Japan, records received data by using the above-mentioned magnetic recording and reproducing apparatus, ends the reception and the recording at another point over Japan a little before the artificial satellite goes round the earth and transmits the received data thus recorded to a ground station in Japan in a short period of time in which the artificial satellite orbits from point to another certain point over Japan as shown in FIG. 1 of the accompanying drawings.
Also, let us consider the case that received data 1 to 40 are sequentially recorded on respective slant tracks at every five data from left to right and also from bottom to top of the slant tracks on a magnetic tape by the above-mentioned magnetic recording and reproducing apparatus as shown in FIG. 2A. Because the received data thus recorded must be reproduced rapidly and transmitted to the ground station, the magnetic tape is not rewound and is transported in the opposite direction at the same speed as that of the recording mode. Then, when recorded data is reproduced at variable speed by a rotary magnetic head that can be displaced in the direction substantially perpendicular to the slant tracks, received data are reproduced in the same order as that of the recording mode in the slant tracks because the rotational direction of the rotary magnetic head is the same as that of the recording mode but reproduced data become discontinuous on the whole of the slant tracks as shown in FIG. 2B.
Therefore, when reproduced data are temporarily stored in a memory and read out in the opposite order, continuous data can be obtained on the whole as shown in FIG. 2C, which requires extra time to write and read data in and from the memory.
It is customary that a conventional data recording apparatus (data recorder) records and reproduces data in a so-called multi-track system in which a plurality of tracks is formed in the longitudinal direction of a magnetic tape serving as a recording medium and data are recorded in these tracks.
When the multi-track system is utilized, data can be recorded and reproduced at an arbitrary speed with ease, and also a so-called reverse direction data reproduction can be carried out with ease in which data is reproduced while the magnetic tape is transported in the direction opposite to that of the recording mode.
The aforesaid reverse direction data playback is utilized in the following case.
FIG. 3 shows the state of a communication between an artificial satellite and a ground station. The artificial satellite shown in FIG. 3 is a resource observation satellite such as LANDSAT or the like. The artificial satellite records various data of digital system picked up by a camera mounted thereon, e.g., video data on a data recorder and transmits this information to the ground station in the form of a radio signal.
In that case, to save time, the above-mentioned artificial satellite reproduces data recorded on the data recorder while the tape is not rewound, i.e., the artificial satellite carries out the aforesaid reverse direction playback and transmits reproduced data to the ground station. Accordingly, data sequence received by the ground station is in the opposite order to that of the recording mode. Further, data speed of data to be transmitted may be varied in accordance with an instruction from the ground station.
As described above, the reverse direction data playback has heretofore been carried out by the multi-track system data recorder. While the multi-track system data recorder can reproduce data at an arbitrary data speed and effect the reverse direction data playback with ease, the multi-track system data recorder is extremely low in recording density as compared with a helical-scan system data recorder that records data on the longitudinal direction of the tape in a helical-scan fashion similar to the recording system of a VTR (video tape recorder) or the like.
For the helical-scan system data recorder, there is proposed a method of playing back a signal in the reverse direction as is described in Japanese laid-open patent publication No. 62-274991. Although data whose sequence is reversed at every field or frame is reconverted in the original data sequence when the data recorder plays back only video data, the data recorder must handle arbitrary data in addition to video data. Hence, the above-mentioned reverse direction signal playback method cannot be applied to the data recorder directly.
Further, the helical-scan system data recorder cannot reproduce data at an arbitrary data speed. Therefore, in order that the data recorder can reproduce data at desired data speed, data that had been recorded on the magnetic tape at data speed inherent in the data recorder is reproduced, and then the above data speed must be converted into an arbitrary data speed by utilizing a buffer memory of a large capacity.